1. Field of the Invention
The present invention relates to a solid image pickup device as well as an image pickup system, and in particular relates to a solid image pickup device as well as an image pickup system having signal amplification means per pixel.
2. Related Background Art
As representatives of solid image pickup devices, there is a CCD image sensor comprising photodiodes and CCD shift-registers and an APS (Active Pixel Sensor) comprising photodiodes and MOS transistors.
The APS comprises per pixel a photodiode, a MOS switch, and an amplifying circuit to amplify a signal from the photodiode and has a lot of advantages such that “XY addressing” and “integration of a sensor and a signal processing circuit into one chip” are possible.
Moreover, in recent years, the APS is attracting attention due to improvement in microfabrication technology for MOS transistors and increased requirement for “integration of a sensor and a signal processing circuit into one chip” and “reduction in power consumption,” etc.
FIG. 28 is a circuit diagram of a solid image pickup device constituting an area image sensor of the prior art. A unit cell 1 corresponding to one pixel has a photodiode 3, a transfer switch Q1, a reset switch Q2, amplifying means Q3, and a selecting switch Q4.
As for electrodes as well as wirings for outputting optical signal, there are:
electrodes 17 as well as selection control lines (selecting switch lines) 7 for selecting unit cells;
electrodes 16 as well as transfer control lines (transfer switch lines) 6 for transferring an electric charge from photodiodes 3 as the photoelectric conversion portions into input terminals of amplifying means;
electrodes 15 as well as reset control lines (reset switch lines) 5 for resetting the input terminals of the amplifying means; and
electrodes 18 as well as signal output lines 8 for outputting signal.
Reference numeral 4 denotes a power line for providing a reference voltage to the amplifying means and the reset switch.
Among these components, except the power lines 4, the three kinds of lines 5, 6, and 7 are disposed in the direction of rows, and the signal output lines 8 are disposed in the direction of columns. In general, these wirings are disposed at the shortest wiring distance as well as at the narrowest line width that can be attained in the manufacturing process so as not to reduce the numerical aperture.
For example, as for the length of those wirings, the length of a wiring per row could reach 10 mm in a sensor with a diagonal distance of 16.93 mm (⅔ inch) and about two million pixels. Further, since the number of rows are approximately 1000, the total length of the control lines will reach 10 m.
However, since the APS has a larger number of elements within one pixel (within one unit cell) as compared with the CCD image sensor, and since the size of a chip has been increased with the tendency of enlargement of the sensor area in recent years, a lowering in the manufacturing yield related to wiring is liable to arise.